Both hydraulic gear pumps and hydraulic gear motors are well-known in the field of hydro-mechanical development. A hydraulic gear motor is a mechanical device which converts hydraulic pressure and flow into torque and angular displacement (rotation). Conceptually, a hydraulic gear motor is the converse of a hydraulic gear pump. A hydraulic gear motor is usually designed for introduction of high-pressure hydraulic fluid at an inlet and egress of hydraulic fluid at a low pressure at a subsequent outlet, so as to convert hydraulic power into rotary mechanical motion on an output shaft to drive a load. A conventional hydraulic gear pump, on the other hand, is designed for low-pressure fluid flow into an inlet and requires high-pressure fluid flow at an outlet.
Hydraulic gear pumps and gear motors are commonly combined to form hydraulic drive systems. One or more hydraulic gear pumps, coupled to one or more hydraulic gear motors, constitute a hydrostatic transmission which today has application in motor vehicles, agricultural and industrial machinery, and in many other mechanical devices and equipment.
The major disadvantage of conventional prior art gear transmissions is that they cannot supply a wide range of gear ratios all in one compact unit.
Another disadvantage is that prior art hydrostatic transmissions are generally connected mechanically to a differential and not directly to the drive wheels of a vehicle where operation would be more efficient.
Yet another disadvantage of prior art hydrostatic transmissions is that hoses, tubes, connectors and adapters are generally required for hydraulic fluid to be transferred between components.